Kinetic studies on reduction of cytochromes P-450 and b5 by dithionite

The kinetics of reduction of cytochromes P-450 and b5 by dithionite had been studied in solution and in microsomal and proteoliposomal membranes by the stopped-flow technique. In all the cases studied the kinetic curves of reduction of cytochrome b5 obey first-order kinetics in relation to cytochrome with the rate constant about 14 s-1 at 10.6 mM dithionite. The kinetic curves of reduction of cytochrome P-450 fit an equation for the sum of two exponentials with the parameters varying from system to system. The simple first-order kinetics of cytochrome P-450 reduction had been observed in the presence of non-ionic detergent Triton N-101. The apparent biphasity of cytochrome P-450 reduction by dithionite should be the result asymmetric distribution of hemoprotein in microsomal and proteoliposomal membranes as well as in cytochrome oligomers in solution.